The Morgan has one of the world's greatest collections of ancient Near Eastern cylinder seals, small stone cylinders finely engraved with images for transfer to clay by rolling.[10] It also contains many music manuscripts and a considerable collection of Victoriana, including one of the most important collections of Gilbert and Sullivan manuscripts and related artifacts.[11]

Of interest to Australians is a copy of the letter written by Andrea Corsali from India in 1516. This letter, one of five in existence, contains the first description of the Southern Cross which is also illustrated by Corsali in this letter and which was also named "croce" by him. One other copy of the letter is in the British Library and two are in Australia. The fifth is in the Library of Princeton University. The letter is also readily available in Ramusio's Viaggi, a compendium of letters of exploration, published in Venice in three volumes from 1555.

The interior of the building is richly decorated, with a polychrome rotunda which leads to three public rooms, which were originally Morgan's private study, the librarian's office, and the library itself.[12] The rotunda itself has a domed ceiling with murals and plasterwork inspired by Raphael, created by H. Siddons Mowbray. Morgan's study, now the West Library, has been called "one of the greatest achievements of American interior decoration," while the East Library features triple-tiers of bookcases.[4]

Morgan's residence was torn down in 1928, after his death, to be replaced by an annex building which featured an exhibition hall and a reading room, designed by Benjamin Wistar Morris to harmonize with McKim's original.[4]

The Italianate brownstone house at Madison Avenue and East 37th Street was built in 1854 by Isaac Newton Phelps and bequeathed to his daughter Helen Stokes, wife of Anson Phelps Stokes.

The remaining Italianate brownstone house in the library complex is 231 Madison Avenue, on the corner of East 37th Street. This house was built by Isaac Newton Phelps who bequeathed it to his daughter, Helen Stokes, wife of Anson Phelps Stokes. She extended the building, doubling the size and adding an additional attic floor (architect R. H. Robertson). Their son, architect Isaac Newton Phelps Stokes, was born in the house on April 11, 1867. The house was purchased by J. P. Morgan in 1904. It served as the home of his heir J. P. Morgan Jr. from 1905 to 1943.[2][13]

The most recent addition to the library is a modernist entrance building designed by Italian architect Renzo Piano – his New York City debut – and Beyer Blinder Belle, which was completed in 2006.[4] Although externally "bland", the building helps to organize the interior spaces of the complex.[2]

The Library was closed during the construction and expansion. In the interim it sponsored numerous traveling exhibitions around the country. When the work was completed, it reopened on April 29, 2006 as the Morgan Library & Museum. With the expansion above and below street level, the Morgan's exhibition space had been doubled; Piano set its new reading room under a translucent roof structure, to allow scholars to examine manuscripts in natural light. Piano's four-story steel-and-glass atrium links McKim's library building and the Morgan house in a new ensemble. Added storage facilities were obtained by drilling into Manhattan's bedrock schist.

Between 1987 and 2008, Charles E. Pierce Jr. served as director of what was then known as the Pierpont Morgan Library.[14] During his tenure at the Morgan Library and Museum between 2008 and 2015, director William M. Griswold spearheaded the growth of its collections, exhibition programs and curatorial departments, adding a photography curator in 2013, a first for the institution. In an effort to reach a younger audience, he also presented many contemporary-art exhibitions and installed temporary sculpture in its atrium.[15] In 2015, the Morgan named Colin Bailey as its new director.[16]